Johannesburg: Nelson Mandela charity trustee Jeremy Ractliffe has resigned after admitting to keeping uncut diamonds he received from British supermodel Naomi Campbell in 1997.

Ractliffe, who was head of the Nelson Mandela Children's Fund (NMCF) at the time, owned up to having the gems after Campbell mentioned them in testimony at The Hague war crimes trial of former Liberian leader Charles Taylor.

Prosecutors had been trying to prove the gems were "blood diamonds" given to Campbell by Taylor after a charity dinner in Johannesburg. The model said she did not know the anonymous donor of the "dirty looking pebbles".

The three precious stones are now in the hands of the South African police, and Ractliffe faces possible charges of being in possession of uncut diamonds without a licence, a crime in South Africa.

"He hasn't been charged yet," said Musa Zondi, a spokesman for the police's elite Hawks unit, adding that investigations were continuing.

Ractliffe said he took the stones from Campbell because he feared she might be breaking the law if she took them out of the country. She had suggested he sell the stones and use the money for good causes, although he thought it more prudent simply to keep them.

"Mr Ractliffe regrets his omission to inform the NMCF of his receipt of the uncut diamonds until now," the Fund said in a statement on his resignation as a trustee of the former South African president's charitable foundation.

Taylor is accused in The Hague of rape, sexual slavery and recruiting child soldiers during wars in Liberia and Sierra Leone. Prosecutors allege he received conflict diamonds from Sierra Leone rebels and used them to buy weapons, which he denies.